Ethylene acidic copolymers such as copolymers of ethylene, methyl acrylate, and an acidic comonomer are known. The acidic comonomer acts as an acid cure site for crosslinking. These copolymers are available from E. I. du Pont de Nemours and Company, Wilmington Del. (DuPont) under the VAMAC trademark.
The acidic copolymers of the prior art may be crosslinked and show good high and low temperature properties, and resistance to hot oils, hydrocarbon and glycol based lubricants, and hot water. See, for example, U.S. Pat. Nos. 3,883,472 and 3,904,588. These properties result in applications such as seals, spark plug boots, hose, damping devices, and cable and wire jacketing. These commercial acidic copolymers have melt indices according to American Society for Testing and Materials, ASTM D-1238 Condition E, in the range from about 2 to about 100 g/10 min. The VAMAC product is elastomeric and has glass transition points (Tg) in the range from about −20° C. to about −45° C. The acidic copolymers of the prior art can be crosslinked at ambient temperature, but solution solids (weight % acidic copolymer in solution) are limited due to the low MI of those acidic copolymers. A low MI corresponds to a high molecular weight and thus high solution viscosity.
It is desirable to extend the utility of such ethylene acid copolymers to potential applications where reversible crosslinking is required, to hot melt adhesive applications, to solution applied acidic copolymer applications, and to provide improved solubility in solvents, improved solution viscosity properties, and improved solid state properties by raising the MI. The present invention provides such ethylene acidic copolymers, a process therefor and processes therewith.